First-time MI solicitation arrest, released without court date , how do I protect myself from charges being filed later?

After seeing escort-related ads on social media, I contacted a person online out of curiosity and went to a location she sent. Before any meeting occurred, police approached me. I cooperated, explained everything, and showed the website. I was arrested, fingerprinted, DNA-sampled, photographed, and held overnight. Next morning, a detective read me my rights. Without an attorney, I answered honestly — admitted it was a mistake, first time, no criminal intent. He said he'd speak to his supervisor to help. I was released with no court date. Booking card lists bond and court file number as "To Be Set." Detective verbally said there would be "no records." Questions: Could charges still be filed later? Could I be re-arrested or summoned? What does "To Be Set" mean? Can records/DNA be expunged? Are diversion options available? Can you contact the prosecutor proactively? Please advise.